Process for the manufacture of vanadium-gallium intermetallic compound



United States Patent Richard Maier, Erlangen, assignor to Siemens-Schuckertwerke Aktiengesellschaft, Berlin Siemensstadt, Germany, acorporation of Germany N0 Drawing. Filed Feb. 3, 1965, Ser. No. 430,196Claims priority, application Germany, Feb. 7, 1964,

S 89,421 6 Claims. (Cl. 75200) My invention relates to apowder-metallurgical process of producing the intermetallic compoundvanadiumgallium V Ga, which possesses superconducting properties and hasa high critical magnetic field.

Superconductors having a high critical magnetic field are increasinglyin demand for the production of comused in the production of strongmagnetic fields.

The intermetallic compound vanadium-gallium with beta-tungstencrystalline structure (V Ga) is of special significance. At 0 K. thiscompound has a critical field strength of at least 300 to 400 kilogauss,its transition temperature being at about 14.5 K.

The conventional powder-metallurgical process of producing intermetalliccompounds is not suitable for the production of vanadium-gallium (V Ga).Such process requires mixing the stoichiometrical quantities of theelements in powdered form, pressing the mixed powder and then sinteringit at about 900 to 1100 C. in vacuum or protective gas. An attempt toproduce V Ga-compound in this manner fails because the gallium powderturns pressing The attempt to immerse and anneal a compressed body ofpure vanadium powder in liquid gallium, likewise fails to havesatisfactory results. Tests have shown that in the marginal region ofthe body, where sufiicient gallium is available, there occurs anexothermic reaction at about 700 C. resulting in the formation of thecompound V Ga while pure vanadium remains in the interior of the body.Even with a very long annealing time, the vanadium reacts only slightlywith the initially formed V Ga compound, since the diffusion path isvery long even in small bodies. The X-ray diffraction spectrum of asample of pressed vanadium powder annealed for 70 hours in liquidgallium at about 1000 C. in a fused quartz anipoule showed essentiallyvanadium and V Ga but very little V Ga.

It is an object of my invention to provide a process [for thepowder-metallurgical production of the intermetallic compoundvanadium-gallium (V Ga), and particular-ly a process affording a goodyield even with relatively short annealing periods.

In accordance with the invention, vanadium powder and V Ga -powder aremixed in the stoichiometric ratio corresponding to the reaction equationThe starting material V G a may be produced, for in- By grinding thedesired V Ga -powder is obtained.

with vanadium powder in the stoichiometric ratio corresponding to thereaction equation:

subjected to a The pressed 0., preferably in vacuum, for about .10 torr.During such heating, water vapor es capes at about 250 C., and hydrogenat about 500 C. Both gases were presumably adsorbed during the pressingstage at the large surface of the powder mixture. A eating period of 30to 60 minutes, for example, is sufficient, but this period is in no waycritical shortened or extended. After degassing, sintered underprotective gas, for example, approximately atmosphere, for about 1 hourat a temperature of about 1300" C. 'The positive pressure of about /2atm. argon serves to example, of

produced, having a weight of a density of 4.87 g./cm. and a spacefilling degree of about The X-ray diagram of the product showed only thereflex diagram of V Ga. No presence of vanadium, gallium, their oxidesand nitrides could be found roentgenographically. The micrograph of a.ground and polished section was essentially of single-phase constitu-=tion. The magnetically measured transition temperature amounted to14.55 K.

Sintered V Ga produced according to the invention is suitable asstarting material for further fabrication into ric ratio correspondingto the equation pressing the mixture to a shaped body, and sintering thebody .at a temperature between 1150 and 1400 C.

2. The process of producing the intermetallic vanadium-gallium compoundV Ga, which comprises mixing vanadium powder and gallium powdersubstantially in the stoichiometric ratio V Ga heating the mixture toabout 700C. to produce V Ga compound, preparing from vanadium powder andpowder made of said V Ga -compound a mixture in the stoichiomet-ricratio corresponding to the equation 13V+V Ga 5V Ga, pressing the lattermixture to a shaped body, and sintering the body at a temperaturebetween 1150 and 1400 C.

of producing the intermetallic vahadium-gallium compound V Ga, whichcomprises mixing the stoichiometthe body C. to degas body at atemperature a 4. The process of producing V Ga compound accord- 600 C.,and thereafter sintering the body in protective ing to claim 1, whereinsaid sintering is effected in a progas at a temperature of about 1300 C.for a period in tective gas. the order of one hour.

.5. The process of producing V Ga compound according to claim '1,wherein said sintering is effected in argon 5 References Cited by theExaminer at a pressure of approximately /2 atmosphere. UNITED STATESPATENTS 6. The :process of producing the in-termetallic vanadi-3,028,341 4/1962 Rosi at um-galliu m compound V Ga, which comprisesmixing 3,084,041 4/1963 Zwler et 75*213 vanadium powder and v Ga -powderin the stoichiomet- 3,196,532 7/1965 g et aL X ric ratio correspondingto the equation 10 13 OTHER REFERENCES V+VzGar 5VaGa Zeitsehrift furPhysik, vol. 151, 1958, pp. 308-310.

pressing the mixture at a pressure of about 5-10 to 10- 10 kilopond perom. to a shaped lbody, heating the body in LEON ROSDOL Examine vacuum toa temperature between about 260 to about 15 R. L. GRUDZIECKI, AssistantExaminer.

1. THE PROCESS OF PRODUCING THE INTERMETALLIC VANADIUM-GALLIUM COMPOUNDV3GA, WHICH COMPRISES MIXING VANADIUM POWDER AND V2GA5-POWDER IN THESTOICHIOMETRIC RATIO CORRESPONDING TO THE EQUATION